USB: serial: ftdi_sio: Add MTP NVM support

On 18/06/18 09:46, Johan Hovold wrote:

On Thu, Jun 14, 2018 at 10:08:46PM +0200, Loic Poulain wrote:

quoted

Most of FTDI's devices have an EEPROM which records FTDI devices
configuration setting (e.g. the VID, PID, I/O config...) and user
data. FT230R chip integrates a 128-byte eeprom, FT230X a 2048-byte
eeprom...

This patch adds support for FTDI EEPROM read/write via USB control
transfers and register a new nvm device to the nvmem core.

This permits to expose the eeprom as a sysfs file, allowing userspace
to read/modify FTDI configuration and its user data without having to
rely on a specific userspace USB driver.

Moreover, any upcoming new tentative to add CBUS GPIO support could
integrate CBUS EEPROM configuration reading in order to determine
which of the CBUS pins are available as GPIO.

I'm not necessarily against the idea, but nvmem core needs to be fixed
so that it can handle hotplugging before this can be considered for
merging.

Right now it just returns -EBUSY from nvmem_unregister(),

Yes, this is the behavior if there are active users/references for the 
nvmem provider.

As this use case seems to have come up more than once. I will take a 
closer look at making nvmem_unregister() return void, but with a BIG 
warn when there are active users.

This is already done in devm_nvmem_register/unregister apis.

I can also suggest you to try devm_nvmem_register().


thanks,
srini


  which results

in all kinds of memory leaks, use-after-frees and crashes when user
space holds the character device open while the device is being
unplugged.

quoted

+static void unregister_eeprom(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+
+	if (priv->eeprom)
+		nvmem_unregister(priv->eeprom);
+}

quoted

@@ -1931,6 +2036,9 @@ static int ftdi_sio_port_remove(struct usb_serial_port *port)
  {
  	struct ftdi_private *priv = usb_get_serial_port_data(port);
  
+#if IS_ENABLED(CONFIG_USB_SERIAL_FTDI_SIO_NVMEM)
+	unregister_eeprom(port);
+#endif
  	remove_sysfs_attrs(port);
  
  	kfree(priv);

Thanks,
Johan

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